The present disclosure relates generally to nanoscale structures, and more particularly to methods for generating a composite pattern including either a prepattern including masking features or the complement to a prepattern including masking features, and a pattern generated through directed self-assembly with frequency multiplication by the prepattern of a self-assembling material, and structures for effecting the same.
Decreasing the critical dimension (CD) and minimum pitch of features in a nanoscale pattern used to fabricate integrated circuits (ICs) increases the density of devices on a chip, which in turn decreases overall cost per device. The self-assembly of block copolymers, polymer blends, or similar self-assembling materials capable of self-assembling to form regular domains is a possible candidate for extending lithographic patterning to smaller CDs and pitches. The domains formed by these self-assembling materials are highly uniform and are intrinsically arranged periodically across at least two adjacent like domains with a spatial period referred to as the characteristic pitch.
Directing this self-assembly using lithographic features results in a denser pattern with greater spatial uniformity than the lithographic pattern used for direction. In chemical epitaxy, an approach to directed self-assembly (DSA) that enables registration of the self-assembled pattern to underlying lithographic layers, a critical requirement for IC fabrication, a self-assembling material is applied to a surface having a chemical pattern layer immediately beneath the self-assembling material composed of nanoscale regions with differing chemical affinity for at least one of the self-assembled domains. The preferred affinity between at least one portion of the pattern at the surface of the chemical pattern layer, the prepattern, and at least one self-assembled domain leads to alignment of the patterns formed by self-assembly according to the prepattern. Some domains with preferred affinity for the prepattern form over and align with features of the prepattern. Domains which do not form over features of the prepattern self-align to those domains that do form over prepattern features, resulting in a pattern of repeating sets of aligned domains in the self-assembling material. By subdividing the pitch of the prepattern features, the spatial frequency of the self-assembled pattern is a multiple of the spatial frequency of the prepattern, where spatial frequency is given by the number of repeating sets of features in a given length. Selective removal of some domains of the self-assembling material creates a mask by which a pattern can be transferred to the underlying substrate.
The resultant pattern that is to be transferred to the substrate possesses areas encompassing periodic features corresponding to individual self-assembled domains with dimensions (both pitch and CD) that may be significantly smaller than the resolution capable with state-of-the-art lithographic tools. However, IC designs include customized elements such as aperiodic, isolated, or discontinuous features. The most straightforward way to fabricate these using DSA is to trim the DSA-generated pattern using subsequent deposition, lithography, and etch steps. Unfortunately, modification of features corresponding to individual domains in the self-assembled pattern is very challenging given the limited resolution of available lithography tools. More critically, the size of individual self-assembled domains useful for patterning is approaching the scale of the overlay error associated with misalignment of the lithographic trim pattern to the self-assembled pattern. Patterning errors of such commensurate scale pose a severe detriment to device performance, reliability, and uniformity.